! PROJECT SUMMARY/ABSTRACT Non-alcoholic fatty liver disease (NAFLD) affects 30-40% of the U.S. population and has an estimated U.S. economic burden of $103 billion per year. NAFLD is also prevalent in children and adolescents, affecting 34.2% of obese individuals and 7.6% of this population overall. Higher-chlorinated polychlorinated biphenyls (PCBs) are implicated in the etiology of NAFLD, however, little is known about the hepatic toxicity potential of lower-chlorinated PCBs, including 3,3?-dichlorobiphenyl (PCB-11), widely detected in environmental and human samples, including in pregnant women. Preliminary research shows that acute developmental exposures to PCB-11 alone do not result in overt toxicological outcomes in zebrafish (Danio rerio), however, it misregulates hepatic-associated genes, stunts liver development, and increases vacuolization in liver tissue. Further, in combination with Aryl hydrocarbon receptor (Ahr) agonists, PCB-11 can either inhibit Cytochrome p4501a (Cyp1a) enzyme activity induced by a model PAH, exacerbating toxicity, or prevent toxicity induced by PCB-126, highlighting the importance of using a mixtures approach. The objective of this proposed study is to investigate the hepatic toxicity of PCB-11 metabolites, which have longer half-lives in vivo for rodents, and in preliminary data of low-dose exposures show increased hepatic lipid deposition in 15-day fish. The central hypothesis of this proposed study is that PCB-11 induced hepatic toxicity is attributed to its metabolites and is associated with a NAFLD liver phenotype during juvenile development. Aim 1 will determine the toxicity contribution of phenolic and sulfate PCB-11 metabolites in 4-day old fish. Aim 2 will assess PCB-11 and PCB-11-Sulfate toxicity in 30-day juvenile stage fish after low-dose chronic single and mixture exposures. The proposed training plan to execute these aims includes learning and/or performing methods such as EROD assays to measure Cyp1a activity, fluorescence microscopy to assess liver development, histopathology, Oil- Red-O staining to assess lipid deposition, and Fluorescence-Activated Cell Sorting (FACS) for fatty acid composition analysis of hepatocytes. In addition, chronic exposures will be carried out using the OECD Fish, Early-Life Stage (FELS) toxicity test (OECD TG 210) to gain practical experience in regulatory toxicity approaches and to increase preparation for the career goal of working as a government scientist to assess the public health impacts of contaminant exposures. This project will yield in vivo mechanistic toxicity data on PCB-11 and its metabolites at several developmental stages to be of use for public health regulators. The sponsor, Dr. Alicia Timme-Laragy, has a record of NIH funding, is a recent mentor of an NIH F32 Postdoctoral Fellow (now a faculty member at San Diego State University), has numerous equipment for fluorescence microscopy, molecular biology and biochemistry work, and is capable of providing the mentorship and guidance needed to accomplish the goals of the proposed project. Further, UMass Amherst is a large R1 research institution and houses several resources, including the Institute for Applied Life Sciences (IALS). !